Method and Tool for Expanding Tubular Members by Electro-Hydraulic Forming

ABSTRACT

An electro-hydraulic forming tool having one or more electrodes for forming parts with sharp corners. The electrodes may be moved and sequentially discharged several times to form various areas of the tube. Alternatively, a plurality of electrodes may be provided that are provided within an insulating tube that defines a charge area opening. The insulating tube is moved to locate the charge area opening adjacent one of the electrodes to form spaced locations on a preform. In other embodiments, a filament wire is provided in a cartridge or supported by an insulative support.

BACKGROUND

1. Technical Field

The present invention relates to electro-hydraulic forming to expand atubular member in a die.

2. Background Art

In electro-hydraulic forming (“EHF”), an electric arc discharge is usedto convert electrical energy to mechanical energy. A capacitor bank, orother source of stored charge, delivers a high current pulse across twoelectrodes that are submerged in a fluid, such as oil or water. Electricarc discharge vaporizes the surrounding fluid and creates shock waves. Aworkpiece that is in contact with the fluid may be deformed by the shockwave to fill an evacuated die.

Electro-hydraulic forming may be used, for example, to form a flat blankinto a one-sided die. The use of EHF for a one-sided die may savetooling costs and may also facilitate forming parts into shapes that aredifficult to form by conventional press forming or hydroformingtechniques. Electro-hydraulic forming also facilitates forming highstrength steel, aluminum and copper alloys. For example, advanced highstrength steel (AHSS) and ultra high strength steel (UHSS) can be formedto a greater extent with electro-hydraulic forming techniques whencompared to other conventional forming processes. Lightweight materials,such as AHSS and UHSS and high strength aluminum alloys are lightweightmaterials that are used to reduce the weight of vehicles.

The use of high strength, lightweight materials is increasing and hasbeen proposed for hydroforming tubes. Tube hydroforming is a well-knowntechnology that is currently used in production. One problem withconventional hydroforming of tubes is that increased pressure isrequired to fill sharp corners in local areas of the tube. The reducedformability of high strength steel and aluminum exacerbates the problemsassociated with forming sharp corners in localized areas of the partswhen compared with forming such parts with mild steel. To form a tubehaving sharp corners, increased pressure is required in the hydroformingliquid that must be applied to all of the internal surfaces of the tube.To withstand the increased pressure, it is necessary to employ hightonnage presses and may require tens of thousands of pounds of pressure.

The above problems are addressed by Applicants' invention as summarizedbelow.

SUMMARY

It is proposed to use electro-hydraulic forming instead of or inaddition to hydroforming to form high strength parts that have sharpcorners in highly formed localized areas. A pair of electrodes can bepositioned inside the tube and a number of sequential discharges may beutilized to form various areas of the tube when using electro-hydraulicforming.

In another embodiment, a single electrode may be moved to variouslocations within the tube and an electric arc discharge may be createdbetween the electrode and part or die that are connected to a secondelectrode.

In yet another embodiment, a plurality of electrodes may be providedwithin the tube and an insulating shield may be moved to permit anelectric arc discharge between one of the electrodes and the tube wall.

In a further embodiment, a discharge wire filament may be provided in awater filled tube cartridge that may be inserted in one or both ends ofthe tubular member. If a discharge wire filament is used, a wider areaof the tube may be formed by the electric arc discharge through thewire.

In yet another embodiment, a discharge wire filament may be held by aninsulating support and placed in contact with a tube wall.

The above embodiments may be inserted in a tubular member from one orboth sides of the tubular member.

The above embodiments are described in detail below with reference tothe attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagrammatic view of a electro-hydraulic tube forming toolwith two electrodes submerged in the tube before forming.

FIG. 1B is a diagrammatic view of a electro-hydraulic tube forming toolwith two electrodes submerged in the tube after forming.

FIG. 2 is a diagrammatic view of the two electrodes of the embodimentshown in FIGS. 1A and 1B.

FIG. 3A is a diagrammatic view of an electro-hydraulic tube forming toolhaving one electrode submerged in the tube with the other electrodebeing connected to the tube or the die before forming.

FIG. 3B is a diagrammatic view of an electro-hydraulic tube forming toolhaving one electrode submerged in the tube with the other electrodebeing connected to the tube or the die after forming.

FIG. 4 is a diagrammatic view of the electrode of the embodiment ofFIGS. 3A and 3B.

FIG. 5 is a diagrammatic view of an electro-hydraulic tube forming toolhaving multiple electrodes and a movable insulation tube.

FIG. 6 is a diagrammatic view of an electro-hydraulic tube forming toolin which a cartridge including a filament is inserted in the tube.

FIG. 7 is a diagrammatic view of an electro-hydraulic tube forming toolhaving a single wire that contacts the tube and is inserted with asupport in a tube.

FIG. 8 is a diagrammatic view of a multiple wire electro-hydraulic tubeforming tool in which one or more wires are positioned in a tube whereinmultiple wires may be used to provide several discharges within thetube.

FIG. 9 is a diagrammatic view of an electro-hydraulic tube forming toolwherein opposite ends of the tube may receive a wire on an insulatingsupport to provide multiple discharges within the tube.

DETAILED DESCRIPTION

Referring to FIGS. 1A and 1B, an electro-hydraulic forming (“EHF”) tool10 is shown diagrammatically to include an upper die 12 and a lower die14. A tubular pre-form 16, or blank, is disposed within the upper andlower dies 12 and 14 and is shown in its unformed condition in FIG. 1Aand is shown in FIG. 1B after forming with the tube conforming to thedie. It should be understood that the tubular pre-form is initiallysmaller than the die cavity, but then expanded as a result of one ormore electro-hydraulic forming discharges to fill the cavity defined bythe upper and lower dies 12 and 14.

A first electrode 18 and a second electrode 20 are inserted within thetubular pre-form 16 and are submerged in water or oil, as is well knownin electro-hydraulic forming processes.

The first and second electrodes 18 and 20 are replaceable and areattached to the distal end of leads 22 that are each covered by aninsulating sleeve 24 to prevent arcing between the leads 22.

An end electrode seal 26 is provided at one of the tool 10 that receivesthe leads 22 and insulating sleeves 24 of the first and secondelectrodes 18 and 20. The end electrode seal 26 seals the tubularpre-form 16 on one end while an end fill seal 28 is provided at theother end of the tubular pre-form 16 to seal the other end thereof. Theend fill seal 28 includes a port 30 through which a fluid, such as oilor water, is provided to the inside of the tubular pre-form 16. Thetubular pre-form 16 is evacuated through the port 30 so that thepre-form 16 is substantially completely filled with the fluid when theEHF tool 10 discharges between the first and second electrodes 18 and20.

After each discharge, additional fluid may be provided through the port30. The fluid is supplied to the tube 16 at a pressure that is less than20 psi to fill the tube. The pressure is released after the tube isfilled. The EHF tool 10 may be discharged multiple times to formdifferent localized areas of the tubular pre-form 16. Multipledischarges between the first and second electrodes 18 and 20 may beprovided within tube 16 in a contoured area 32 where sharp corners maybe required to be formed in the tubular member 16.

A stored charge circuit 36, or pulse generator, is illustrated inFIG. 1. The stored charge circuit 36 is connected to the lead 22. Toperform an electro-hydraulic forming cycle, the stored charge circuit 36is actuated to create a discharge between the first and secondelectrodes 18 and 20. After the tubular pre-form 16 is fully formed, thefluid is drained through the port 30 and the die may be opened forremoval of the fully formed pre-form 16.

A linear drive 38 is provided to move the electrodes 18 and 20 withinthe tubular member 16. The linear drive 38 may be a hydraulic cylinder,a pneumatic cylinder or motor drive that is capable of moving the firstand second electrodes 18 within the tubular pre-form 16. The lineardrive 38 moves the electrodes 18 and 20 within the contoured area 32 tobe formed by the EHF tool.

As shown in FIG. 2, when the electrodes 18 and 20 are positionedadjacent to an area to be formed, the electrodes 18 and 20 aredischarged in a discharge zone 40. The charge is conducted from thestored charge circuit 36 through the leads 22 to the first and secondelectrodes 18 and 20. An arc is formed between the first and secondelectrodes 18 and 20 in the discharge zone 40.

Referring to FIGS. 3A, 3B and 4, an alternative embodiment of an EHFtool 50 is shown to include an upper die 52 and a lower die 54. Atubular pre-form 56 is received between the upper and lower dies 52 and54. A single replaceable electrode 58 is inserted within the tubularpre-form 56. The electrode 58 is provided with an insulating block 60that insulates the electrode 58 and prevents electrode 58 fromcontacting the wall of the tubular pre-form 56. An insulating sleeve 62is also provided to prevent arcing between the lead 63 and the tubularmember 56. A second lead 64 may be connected to the upper die 52 orlower die 54 of the EHF tool 50. As shown, the electrode 58 is thepositive electrode, while lead 64 is the negative electrode. It shouldbe understood that the polarity of the electrodes can be reversed.

An end electrode seal 66 is provided within one end of the tubularmember 56 to provide a seal between the tubular member and theinsulating sleeve 62 of the lead 63.

An end fill seal 68 is provided at the opposite end of the tubularpre-form 56 that seals the end of the tubular pre-form 56 when the EHFtool 50 is discharged. A port 70 may be received within the end fillseal 68. Fluid may be introduced into the tubular pre-form 56 throughthe port 70. If the fluid is water, it should be understood that it maybe an emulsion of water and a rust preventative. In addition, air may beevacuated through the port 70 to assure complete filling of the tubularpre-form 56 with the fluid. When the forming cycle is complete, the port70 may be used to drain the fluid from the tubular pre-form 56.

A contoured area 72 is shown provided in which the tubular pre-form 56is intended to be expanded by the EHF tool 50.

Referring to FIG. 3, a stored charge circuit 76, or pulse generator, isshown as it is connected to the ends of the leads 63 and 64. The storedcharge circuit 76 is preferably a capacitive charge storage device, asis well known in the art. Alternatively, an inductive charge storagedevice may be used instead of the capacitive charge storage device.

With continuing reference to FIG. 3A, a linear drive 78 is shownengaging the electrode 63. The linear drive 78 is used to move theelectrode within the tube 56, especially in the contoured area 72 toprovide an EHF pulse when the stored charge circuit 76 is actuated. Adischarge zone 80 is also shown in FIG. 3 where the electrode 58 arcs tothe inside of the tubular pre-form 56. The pressure created by the arccreates a shockwave that forms the tubular pre-form against the upperand lower dies 52 and 54.

Referring to FIG. 4, the lead 63 and a replaceable tip 58 is shown ingreater detail. The lead 63 is enclosed by insulating sleeve 62. Theinsulating sleeve 62 may extend to the electrode 58 and also may coverthe distal end of the electrode to partially insulate, or shield, theelectrode. A threaded hole 84 may be provided in the end of the lead 63.In addition, a threaded end 86 may be provided on the lead and a bolt 88may be inserted through the electrode 58 to secure the electrode 58 tothe threaded end 86. Advantageously, the threads of the threaded hole 84and the threaded end 86 of the lead 63 may be of different pitch toeffectively lock the electrode 58 on the end of the lead 63.

As is also shown in FIG. 4, the insulation block 60 prevents contactbetween the electrode 58 and the tube 56. The insulation block 60 andinsulating sleeve 62 prevent any discharges between the lead 63 and thetubular member 56 along the length of the lead 63.

Referring to FIG. 5, an alternative embodiment of an EHF tool 90 isshown that includes a tubular pre-form 92, or blank, in which aplurality of electrodes 94 are inserted. The electrodes 94 are securedto a lead 96. The tubular preform 92 is connected to lead 98. Aninsulating sleeve 100 and an insulating spacer 102 are provided on thelead 96 to prevent inadvertent discharge between the lead 96 and thewall of the tubular pre-form 92. An insulation tube 106 is providedbetween the lead 96 and the tubular pre-form 92. The insulation tube 106is operatively connected to a linear drive 107. The insulation tube 106defines a charge area opening 108.

The insulation tube 106 prevents arcing between any of the electrodes 94except where the electrode 94 is disposed adjacent to the charge areaopening 108. A discharge area 110 is illustrated diagrammatically by anarrow indicating where the arc is formed between one of the electrodes94 and the tubular pre-form 92 through the charge area opening 108. Theinsulation tube 106 prevents arcing between the other electrode 94 andthe tubular pre-form 92. The insulation tube 106 is movable to locatethe charge area opening 108 adjacent to at least one of the electrodes94. The insulation tube 106 is movable to permit the tool 90 to act uponseveral locations within the tubular pre-form 92.

Referring to FIG. 6, another alternative embodiment is shown in which atube 116 may be acted upon by an EHF tool, including an upper and alower die that are not shown in FIG. 6. However, it should be understoodthat the EHF tool including an upper and lower die as described withreference to FIGS. 3-4 may be used with the cartridge 118 shown in FIG.6. The cartridge 118 includes an insulator tube 120 and a filament wire122. A support 126 is provided to support the filament wire 122 withinthe insulator tube 120. Fluid 128 is provided both within the cartridge118 and between the cartridge 118 and the tube 116.

The filament wire 122 is connected to a positive polarity connection 130and a negative polarity connection 132 on opposite ends. The cartridge118 may be inserted into the tube 116. A stored charge circuit, such asthat disclosed in FIG. 3, is provided to generate an electrical pulsethat is provided to the filament wire 122. Upon actuation of the storedcharge circuit, the pulse vaporizes the filament wire 122 creating anarc and a shockwave through the fluid 128 causing the tube 116 to beexpanded into engagement with the upper and lower die of the EHF tool.The filament 122 may be coiled or otherwise retained between a support126 and the cartridge 118.

Referring to FIG. 7, another alternative embodiment is diagrammaticallyshown wherein a tube 146 is provided in an EHF tool having an upper andlower die similar to that illustrated in FIG. 3. The discharge wire 148is inserted from one end of the tube and supported by an insulating wiresupport 150. As previously described, the tube 146 would be filled withfluid and the discharge wire is submerged within the fluid. One end ofthe discharge wire 148 is placed in contact with the tube 146 at a wallcontact point 152. A negative return 154, or ground, is connected to thetube 146.

The discharge wire and negative return 154, or ground, are operativelyconnected to the stored charge circuit, as previously described withreference to FIG. 3. Upon actuation of the stored charge circuit 76, theelectrical discharge through the discharge wire 148 completes thecircuit through the tube 146. Upon actuation of the stored chargecircuit, the discharge wire is vaporized creating an arc that in turncreates a shockwave that forces the tube 146 into engagement with theupper and lower dies of the EHF tool.

Referring to FIG. 8, another alternative embodiment is shown in which atube 168 receives a first wire 170 and a second wire 172 on a wiresupport 174. As described previously with reference to FIG. 3, an EHFtool including an upper die and a lower die and a stored charge circuitwould also be included as part of this embodiment. An insulating support174 supports the first and second wires to permit multiple dischargeswithin the tube 168.

Upon a first actuation of the stored charge circuit, the first wire 170receives the discharge and vaporizes to generate a shockwave to drivethe wall of the tube 168 into engagement with the die. A second pulsemay be provided by the stored charge circuit to the second wire 172 toprovide a further forming operation on the tube wall. The insulating andisolating support 174 may be moved within the tube if desired to providean electro-hydraulic forming pulse in a range of locations within thetube 168. While two wire loops are shown, it should be understood thatmore wires could be provided within the scope of the invention.

Referring to FIG. 9, a tube 178 is shown that may be formed according toa further embodiment of this disclosure. In this embodiment, a firstwire 180 is supported by a first support 182. The first wire 180 andfirst support 182 are inserted through a first end 184 of the tube 178.A second wire 186 supported by a second support 188 is inserted from asecond end 190 of the tube 178. In this embodiment, both ends of thetube are used to receive one of the wires 180, 186 from opposite ends.

The concept of providing a wire through opposite ends or of providing anelectrode assembly to opposite ends of the tube may be implemented withany previously described embodiments with minor modification. It wouldbe necessary to incorporate an end fill seal and port in one or both ofthe seals provided at the ends of the tube. By permitting the electrodeor electrodes to be inserted from opposite ends of the tube, difficultto reach areas may be accessed by the EHF tool.

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, and it isunderstood that various changes may be made without departing from thespirit and scope of the invention.

What is claimed:
 1. A tool comprising: a die into which a tubular memberis inserted; a fluid provided within the tubular member; a set ofelectrodes, wherein at least one of the electrodes is submerged in thefluid; a drive mechanism that moves at least one of the electrodesrelative to the tubular member; an energy storage device electricallyconnected to the electrodes that provides a plurality of electricaldischarges to form the tubular member into the die.
 2. The tool of claim1 wherein the set of electrodes further comprises a dual electrodeassembly having at least two electrodes that are inserted within thetubular member.
 3. The tool of claim 2 wherein the dual electrodeassembly is moved within the tubular member.
 4. The tool of claim 2wherein two dual electrode assemblies are inserted into the tubularmember with a first dual electrode assembly being inserted in a firstend of the tubular member and a second dual electrode assembly that isinserted in a second end of the tubular member.
 5. The tool of claim 2wherein the dual electrode assembly includes first and second leads thatare each provided with insulation to prevent electrical dischargesbetween the leads and that are connected to the energy storage device.6. The tool of claim 5 wherein the leads have sufficient stiffness toallow then to be advanced through the tubular member and must besufficiently flexible to conform to any bends in the tubular member. 7.The tool of claim 2 wherein the dual electrode assembly includes a pairof leads and a pair of replaceable tips that are securely fastened tothe leads.
 8. The tool of claim 1 wherein the fluid is supplied to thetubular member at a pressure that is less than 20 psi to fill the tube,and wherein the pressure may be released after the tube is filled.
 9. Atool for forming a tubular part comprising: a tubular member; a die intowhich the tubular member is inserted; a first electrode inserted withinthe tubular member; a second electrode electrically connected to thetubular member; a fluid provided within the tubular member and in whichthe first electrode is immersed; a linear drive mechanism connected tothe first electrode that moves the first electrode in a linear pathrelative to the tubular member; and an energy storage device; acontroller that discharges the energy storage device to provide aplurality of electrical discharges between the first and secondelectrodes through the fluid; and wherein the electrical discharges forma plurality of axially spaced areas of the tubular member into the die.10. The tool of claim 9 further comprising an insulator block disposedabout the first electrode that spaces the electrode from the tubularmember and insulates the first electrode from the tubular member. 11.The tool of claim 9 wherein the first electrode is connected to theenergy storage device by a lead that is provided with insulation toprevent electrical discharges between the first electrode and the secondelectrode.
 12. The tool of claim 9 wherein the first electrode isadvanced from one end of the tubular member to the other.
 13. The toolof claim 9 wherein the first electrode is provided with an electrode tipthat is a circular disk shaped member having a pointed outercircumference.
 14. A tool for forming a tubular part comprising: atubular member; a die into which the tubular member is inserted; anelectrode having a first polarity electrically connected to the tubularmember; a plurality of electrodes having a second polarity inserted ataxially spaced locations within the tubular member; a fluid providedwithin the tubular member and in which the electrodes having a secondpolarity are immersed; a sleeve that insulates between the electrodehaving the first polarity and the electrodes having a second polarity,the sleeve defining at least one discharge area in which the sleeve doesnot insulate between the electrode having the first polarity and theelectrodes having a second polarity; a linear drive mechanism that movesthe sleeve in a linear path relative to the tubular blank and theelectrodes having a second polarity; and an energy storage device; and acontroller that discharges the energy storage device to provide aplurality of electrical discharges through the at least one dischargearea between the electrode having the first polarity and the electrodeshaving a second polarity through the fluid that forms a plurality ofaxially spaced areas of the tubular member into the die.
 15. The tool ofclaim 14 wherein the plurality of electrodes having a second polarityare connected to a lead that is connected to the energy storage device.16. The tool of claim 15 wherein only one discharge area is provided inthe sleeve, and wherein the sleeve is moved by the linear drivemechanism to align the discharge area with one of the plurality ofelectrodes having a second polarity to create a preferential dischargecondition for the one electrode.
 17. The tool of claim 16 wherein thelinear drive mechanism moves the sleeve axially through the tubularmember to position the discharge area to be aligned with each of theplurality of electrodes at different times to provide a plurality ofaxially spaced locations to form the tubular member in a plurality ofareas.
 18. A tool for forming a tubular part comprising: a tubularmember; an electro hydraulic forming (EHF) die into which the tubularmember is inserted; an electrode assembly having an electrode wirehaving a positive lead and a negative lead, the electrode wire isdisposed within a cartridge that is filled with a first volume of fluid,the assembly is inserted within the tubular member, a second volume offluid is provided within the tubular member and the dual electrodeassembly is submerged in the second volume of fluid; an energy storagedevice; and a controller that discharges the energy storage device toprovide an electrical discharge to the positive lead and the negativelead of the electrode wire in the electrode assembly that provides ashock wave that passes through the fluid to conform the tubular memberwith the EHF die.
 19. The tool of claim 18 wherein the electrode wire ishelically coiled and extends in two segments that extend substantiallythe full length of the cartridge, the two segments are connected one toeach of the leads.
 20. The tool of claim 19 further comprising aninsulator that is disposed between the two segments of the wire exceptat a distal end of the wire where the two segments are reversely turnedrelative to each other.
 21. The tool of claim 18 wherein the cartridgeis a plastic tube that is destroyed when the electrical discharge isprovided.
 22. A tool for forming a tubular part comprising: a tubularmember; an electro hydraulic forming (EHF) die into which the tubularmember is inserted, the EHF die is connected to a first electrode havinga first polarity; an electrode assembly having an electrode wire that isconnected to a second electrode having a second polarity, a supportmember supports the electrode wire within the EHF die, the assembly isinserted within the tubular member with the electrode wire contactingthe EHF die at a distal end thereof; a volume of fluid is providedwithin the tubular member, and wherein the electrode assembly issubmerged in the fluid; an energy storage device; and a controller thatdischarges the energy storage device to provide an electrical dischargebetween the first and second electrodes that arcs through the electrodewire and provides a shock wave that passes through the fluid to conformthe tubular member with the EHF die.